In June 2015, he became the first SMU Mustang to win the NCAA individual championship, recording a score of 280 (−8) to win by one stroke. In August, he won the U.S. Amateur title, defeating Derek Bard 7 & 6 in the 36-hole final. He became the fifth player to win both the NCAA and U.S. Amateur titles in the same year, joining Jack Nicklaus (1961), Phil Mickelson (1990), Tiger Woods (1996), and Ryan Moore (2004).
Masters Tournament: Finished runner-up at the Masters, one stroke behind Patrick Reed, for his best result at the event. For the first time in eight starts at Augusta National, recorded four par-or-better rounds (70-72-65-67). Earned his third runner-up in a major (2nd/2018 Masters Tournament, T2/2014 The Open Championship, T2/2014 U.S. Open) and third top-five in the last four (2nd/2018 Masters Tournament, T5/2017 Open Championship, T5/2017 U.S. Open). With third-round 65, was one of just four players to post a bogey-free round during the week (Rory McIlroy/65, Jon Rahm/65, Si Woo Kim/65) with all four occurring in the final round.
BMW Championship: At No. 22 in the FedExCup standings heading into the third Playoffs event, the BMW Championship, he bogeyed No. 17 in a final-round even-par 72 to miss advancing to the TOUR Championship by half a point, finishing the season No. 31 in the FedExCup standings. Charl Schwartzel fired a final-round 8-under 64 to claim the No. 30 position.
DeChambeau made his PGA Tour debut as an amateur in June 2015 at the FedEx St. Jude Classic near Memphis, Tennessee, and finished in 45th place. He played in his first major championship at the U.S. Open at Chambers Bay, but missed the cut by four strokes. DeChambeau was unable to defend his NCAA title in 2016 after the SMU athletic department was handed a postseason ban by the NCAA. He decided to forgo his senior season to play in a number of events before turning professional. At the 2015 Australian Masters in November, DeChambeau was runner-up with John Senden and Andrew Evans, two shots behind the winner Peter Senior. He was the low amateur at the Masters in 2016 and tied for 21st place.
In July 2011, Fowler tied the 54-hole lead at the AT&T National, but an early double bogey on Sunday derailed his opportunity for his first PGA Tour win. Two weeks later Fowler finished tied for 5th in The Open Championship at Royal St George's. In August, Fowler finished in a tie for second at the WGC-Bridgestone Invitational behind winner Adam Scott, lifting him to 28 in the world rankings.
Hyundai Tournament of Champions: Finished T6 in a Monday-start-Tuesday-finish event, the season-opening, 54-hole Hyundai Tournament of Champions. The event "started" twice during the regularly scheduled first round Friday and later Sunday, but both times PGA TOUR rules staff halted play due to unplayable windy conditions and subsequently voided all scores that had taken place. As the first player off the tee, he ended up hitting three "opening" shots of the season.